Common mobile terminals are designed around a processing core, wherein terminal software (SW) is running on said processing core.
Tracing, testing, tuning and debugging terminal SW is very difficult using only normal output devices such as display or serial interfaces that come out of the processing core, i.e. out of the terminal processor.
Therefore the terminal processors have dedicated interfaces for tracing, testing, tuning and debugging. They are frequently used during the R&D phase but also after the product is on the market, but, when product matures and the terminal is put inside its actual mechanics, these tracing, testing, tuning and debug interfaces are left inside these covers in order to prevent accessing them anymore. If some bug or fail is discovered at the late phase of the project, it is difficult to trace, test, tune or debug the soft- and hardware since there is no access to these trace, test, tune&debug interfaces without hardware modifications.
For instance, in some mobile terminals the trace, test, tune &debug connections are routed under the battery, and if someone wants to use them a special battery and a jig are required. This use of a special battery and jig is only suited for laboratory conditions, but trace, test, tune &debugging in the field is not that easy. Furthermore, a specific extra connector to sales terminal just for trace, test, tune &debug purpose is not feasible.
On the other hand, for instance, network operators require products having such tracing capabilities to test their networks or third party SW developers may require such products for testing their SW.